Mesoporous carbon composite containing carbon nanotube

ABSTRACT

Provided are a CNT-mesoporous silica composite, a CNT-mesoporous carbon composite, a supported catalyst using the CNT-mesoporous carbon composite as a support, and a fuel cell using the supported catalyst as the anode, cathode, or both anode and cathode. The CNT-mesoporous carbon composite is prepared using the CNT-mesoporous silica composite. The CNT-mesoporous carbon composite has a high electrical conductivity due to the CNTs contained therein, and thus, when the CNT-mesoporous carbon composite is used in an electrode of a fuel cell, the fuel cell has a remarkably improved performance relative to the conventional catalyst support which does not contain CNTs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/944,706 filed Nov. 11, 2010, which is a divisional of U.S. patentapplication Ser. No. 11/265,177, filed Nov. 3, 2005, and claims priorityto and the benefit of Korean Patent Application No. 10-2004-0089211,filed on Nov. 4, 2004, which are all hereby incorporated by referencefor all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carbon nanotube (CNT)-mesoporouscarbon composite, a method of preparing the same, a supported catalyst,and a fuel cell, and more particularly, to a CNT-mesoporous carboncomposite prepared using a CNT-mesoporous silica composite as atemplate, a method of preparing the CNT-mesoporous carbon composite, ais supported catalyst using the CNT-mesoporous carbon composite as asupport, and a fuel cell using the supported catalyst as an anode,cathode, or both anode and cathode.

2. Discussion of the Background

Fuel cells are clean energy sources that have received considerableinterest as one of the alternatives for replacing fossil fuels.

A fuel cell is a power generating system that produces direct currentelectricity through an electrochemical reaction of fuel, such ashydrogen, natural gas, or methanol, with an oxidizing agent. In general,the fuel cell includes an anode (fuel electrode) where a supplied fuelis electrochemically oxidized, a cathode (air electrode) where theoxidizing agent is electrochemically reduced, and an electrolytemembrane which is interposed between the anode and the cathode toprovide a path for transporting ions produced at the anode to thecathode. Electrons are generated through the oxidation of the fuel atthe anode, work via an external circuit, and are then returned to thecathode to reduce the oxidizing agent. A fuel cell's catalyst iscontained in the anode and the cathode and catalyzes the electrochemicalreaction. Thus, many trials have been conducted to increase the activityof the catalyst used in the electrodes. The catalytic activity increasesas the reaction surface area of the catalyst increases. Reaction surfacearea increases as the particle diameter of the catalyst decreases, andsmall particle diameter allows the catalyst particles to be uniformlydistributed on the electrode. Where reaction surface area of thecatalyst is increased, the surface area of the catalyst support shouldalso be increased.

A catalyst support for the fuel cell should have a large surface areadue to high porosity and a high electrical conductivity for the flow ofelectrons. Amorphous microporous carbon powders known as activatedcarbon or carbon black are widely used as catalyst support for the fuelcells.

Amorphous microporous carbon powders are generally prepared bychemically and/or physically activating a raw material, such as wood,peat, charcoal, coal, brown coal, coconut peel, and petroleum coke.After activation, the carbon has a pore size of about 1 nm or less and aspecific surface area of about 60 m²/g to about 1000 m²/g. Specifically,Vulcan Black and Ketjen Black, which are commercial products widely usedas catalyst support for fuel cells, have a specific surface area ofabout 230 m²/g and about 800 m²/g, respectively. Their primary particlediameter is about 100 nm or less.

However, the amorphous microporous carbon particles have poorinterconnection of micropores. In particular, in a conventional directmethanol fuel cell (DMFC), a supported catalyst using the amorphousmicroporous carbon particles as a support has lower reactivity than acatalyst consisting only metal particles. However, using a catalystconsisting of only metal particles increases the cost of the DMFCsignificantly. Thus, the development of a carbon support capable ofimproving the reactivity of the catalyst without incurring the cost of apure metal catalyst is required.

To overcome these problems, a mesoporous carbon molecular sieve isdisclosed in Korean Patent Laid-Open Publication No. 2001-0001127. Thispatent discloses a method of preparing an ordered mesoporous carbonmolecular sieve using a mesoporous silica, which is prepared using asurfactant as a template material. In the above method, based onnano-replication, the mesoporous silica, such as “MCM-48” and “SBA-1”,has micropores connected three-dimensionally by mesopores and is used asa template to prepare an ordered mesoporous carbon molecular sieve withmicropores and mesopores, which have a uniform diameter and areregularly arranged. According to the definition of the InternationalUnion of Pure and Applied Chemistry (IUPAC), micropores refer to poreswith a diameter of less than 2 nm and mesopores is refer to pores with adiameter of 2 to 50 nm.

However, since the mesoporous carbon sieve is composed of amorphouscarbon, it has a relatively low electrical conductivity. Therefore,there is a need to improve the electrical conductivity of the supportand thus improve the performance of the fuel cell.

SUMMARY OF THE INVENTION

The present invention provides a carbon nanotube (CNT)-mesoporous silicacomposite and a method of preparing the same.

The present invention also provides a CNT-mesoporous carbon compositefor improving the performance of a fuel cell and a method of preparingthe same.

The present invention also provides a supported catalyst in which metalcatalyst particles are uniformly supported on the CNT-mesoporous carboncomposite.

The present invention also provides a fuel cell using the supportedcatalyst as the cathode, the anode, or both the cathode and the anode.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses a carbon nanotube (CNT)-mesoporoussilica composite comprising CNTs and mesoporous silica.

The present invention also discloses a method of preparing aCNT-mesoporous silica composite, comprising the steps of: dissolving asurfactant in water and adding CNTs to form a mixture, adding a silicasource and water to the mixture to form a solution, adding an acid tothe solution to adjust the pH, stifling the solution, heating thesolution to obtain powders, is separating the powders from the solution,washing the powders, and calcining the washed powders.

The present invention also discloses a CNT-mesoporous carbon compositecomprising CNTs and mesoporous carbon.

The present invention also discloses a method of preparing aCNT-mesoporous carbon composite, comprising the steps of: preparing acarbon precursor sol by mixing a polymerizable carbon-containingcompound with a carrier, impregnating the CNT-mesoporous silicacomposite with the carbon precursor sol, polymerizing the carbonprecursor sol impregnated into the CNT-mesoporous silica composite toobtain a carbon precursor, thermally decomposing the carbon precursor toobtain a carbon structure, and treating the carbon-CNT-silica compositeimpregnanted with the carbon structure with a solution capable ofselectively dissolving silica to remove the silica.

The present invention also discloses a supported catalyst comprising aCNT-mesoporous carbon composite and metal catalyst particles uniformlysupported on the CNT-mesoporous carbon composite.

The present invention also discloses a fuel cell comprising a cathode,an anode, and an electrolyte membrane interposed between the cathode andthe anode, where either the cathode, the anode, or both the cathode andanode comprises the supported catalyst.

The CNT-mesoporous carbon composite has a high electrical conductivitydue to the CNTs contained therein. Thus, when the CNT-mesoporous carboncomposite is used as a catalyst support in an electrode of a fuel cell,it provides a remarkably improved performance of the fuel cell relativeto the conventional catalyst support, which does not contain CNTs.

It is to be understood that both the foregoing general description andthe is is following detailed description are exemplary and explanatoryand are intended to provide further explanation of the invention asclaimed

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1A is a scanning electron microscopic (SEM) photo of a carbonnanotube (CNT)-mesoporous silica composite prepared using a methodaccording to an embodiment of the present invention;

FIG. 1B is a transmission electron microscopic (TEM) photo of aCNT-mesoporous silica composite prepared using a method according to anembodiment of the present invention.

FIG. 2A illustrates X-ray diffraction (XRD) graphs of a CNT-mesoporoussilica composite (Example) prepared according to an embodiment of thepresent invention and a mesoporous silica material prepared without CNTs(Comparative Example);

FIG. 2B illustrates XRD graphs of a CNT-mesoporous carbon composite(Example) prepared according to an embodiment of the present inventionand a mesoporous carbon material prepared without CNTs (ComparativeExample);

FIG. 3 illustrates XRD graphs of a CNT-mesoporous silica composite, acombination of a CNT-mesoporous silica composite and a carbon-CNT-silicacomposite before removing the silica, and a CNT-mesoporous carboncomposite after removing the silica is according to an embodiment of thepresent invention;

FIG. 4 illustrates XRD graphs of supported catalysts prepared accordingto an embodiment of the present invention (Example), and supportedcatalysts prepared without CNTs in the support composite (ComparativeExample); and

FIG. 5 illustrates graphs of cell potential vs. current density of fuelcells prepared according to an embodiment of the present invention(Example) and fuel cells prepared without CNTs in the catalyst supportcomposite (Comparative Example).

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough, and will fully convey the scope of the invention to thoseskilled in the art.

In an embodiment of the present invention, first a carbon nanotube(CNT)-mesoporous silica composite is prepared, and then a CNT-mesoporouscarbon composite is prepared using the CNT-mesoporous silica compositeas template. The CNT-mesoporous carbon composite is in the form of aporous particle substantially composed of carbon. Unlike a conventionalamorphous microporous carbon powder having primarily micropores, theCNT-mesoporous carbon composite has both mesopores and micropores in anappropriate ratio.

Pores of the CNT-mesoporous carbon composite may or may not be regularlyarranged. In the CNT-mesoporous carbon composite, microporesinterconnect via mesopores or mesopores interconnect via micropores.Accordingly, reactants can be easily supplied to micropores viamesopores, and products created in micropores can be easily dischargedoutside of supported catalyst particles through mesopores.

The CNT-mesoporous carbon composite may be characterized by an averagediameter of mesopores or a surface area.

In the CNT-mesoporous carbon composite, the mesopores may have anaverage diameter of about 2 nm to about 10 nm. If the average diameterof the pores is less than 2 nm, the fuel material supplied cannot beeasily diffused, thereby reducing the catalytic activity. If the averagediameter of the mesopores is greater than 10 nm, the specific surfacearea is decreased, thereby reducing the reaction surface area and, thus,the catalytic activity.

The CNT-mesoporous carbon composite may have a specific surface area ofabout 800 m²/g or greater, and usually about 1000 m²/g to about 3500m²/g. If the specific surface area of the CNT-mesoporous carboncomposite is less than about 800 m²/g, the catalyst metal particles maynot be uniformly dispersed during preparation of supported catalyst. Ifthe specific surface area of the CNT-mesoporous carbon composite isgreater than about 3500 m²/g, too many micropores are present anddiffusion of the fuel may be reduced, thereby reducing the catalyticefficiency.

As described above, the CNT-mesoporous carbon composite is prepared bypreparing a CNT-mesoporous silica composite, impregnating the CNT-silicacomposite with a carbon precursor sol, and then dissolving and removingthe silica.

A method of preparing a CNT-mesoporous silica composite according to anembodiment of the present invention will now be described.

First, a surfactant is dissolved in water and mixed with CNTs. Theconcentration of the surfactant can be about 1,000 to about 100,000parts by weight based on 100 parts by is weight of the CNTs. The CNTsmay be single-walled CNTs (SWNTs), multi-walled CNTs (MWNTs), or carbonnanofibers CNTs.

Then, a silica source is added to the mixture. The concentration of thesilica source can be about 3,000 to about 300,000 parts by weight basedon 100 parts by weight of the CNTs. Then, water is added, and theresultant solution may be about 5,000 to about 500,000 parts by weightbased on 100 parts by weight of the CNTs. The silica source may bealkoxysilane, which is not specifically limited and may betetraethoxysilane (TEOS) or tetramethoxysilane, or alternatively thesilica source may be an aqueous sodium silicate solution. Theconcentration of sodium silicate in the aqueous sodium silicate solutionmay be about 10% to about 30% by weight.

Next, an acid is added to the resultant solution to adjust the pH of thesolution. The acid is not specifically limited and may be nitric acid,hydrochloric acid, sulfuric acid, or acetic acid. The pH of the solutionmay be adjusted from about −0.7 to about 7.0.

Next, the resultant solution is thoroughly mixed by stirring, and thenreacted by heating in an oven. The heating temperature of the oven maybe about 80° C. to about 160° C. If the heating temperature is less thanabout 80° C., the resultant solution may not be sufficiently hydrolysedand thus, the product may have a weak structure. If the heatingtemperature is greater than about 160° C., the desired structure may notbe formed. The reaction time is not specifically limited and can beselected according to the reaction conditions such that an appropriateyield can be obtained. Generally, the heating time may be about 30minutes to about 2 hours. The resultant product is a turbid liquidwithin which white powders are distributed.

Then, the powders are separated from the turbid liquid using aconventional method, such as filtration and centrifuging. After theseparation of the powders, the powders may is be washed at least once.

After the washing, the powders are dried and then calcined in a reactionfurnace to obtain a CNT-mesoporous silica composite. The drying of thepowders may be performed at room temperature for about 12 hours to about36 hours. The calcination temperature of the dried powders may be about300° C. to about 550° C. If the calcination temperature is less thanabout 300° C., a skeletal structure of the template may not be wellformed since impurities may remain. If the calcination temperature isgreater than about 550° C., the skeletal structure may not be uniformand the CNTs in the composite may be combusted. The calcination may beperformed under an oxidizing atmosphere such as air. The calcination maybe performed for about 3 hours to about 15 hours. If the calcinationtime is less than about 3 hours, impurities may remain. If thecalcination time is greater than about 15 hours, a lot of time may bespent during the preparation of the CNT-mesoporous silica composite.Therefore, it may be economically desirable to maintain the calcinationstime at about 15 hours or less.

The concentration of the CNTs in the CNT-mesoporous silica composite maybe about 0.3% to about 10% by weight. If the concentration of the CNTsin the CNT-mesoporous silica composite is less than about 0.3% byweight, an increase of the electrical conductivity over carbon supportwithout CNTs may not result. If the concentration of the CNTs in theCNT-mesoporous silica composite is greater than about 10% by weight, theCNTs may not be uniformly dispersed, and thus the CNT-mesoporous silicacomposite may not be easily prepared.

The CNT-mesoporous silica composite thus prepared is used as a templateto prepare the CNT-mesoporous carbon composite.

A method of preparing a CNT-mesoporous carbon composite according to anembodiment of the present invention will now be roughly described.First, a carbon precursor sol is prepared by mixing a polymerizablecarbon-containing compound with a carrier. Next, the carbon precursorsol is impregnated into the CNT-mesoporous silica composite. Then, acarbon precursor is obtained by polymerizing the carbon precursor sol inthe CNT-mesoporous silica composite. Next, the carbon precursor and theCNT-mesoporous silica composite undergo thermal decomposition, resultingin a carbon-CNT-silica composite. Finally, the silica is dissolved andremoved, and the CNT-mesoporous carbon composite remains.

The carbon precursor is filled in the pores of the CNT-mesoporous silicacomposite as the template. The term carbon precursor refers to amaterial that can be carbonized by thermal decomposition. The carbonprecursor may be a polymer of a polymerizable carbon-containingcompound. The polymerization includes various types of polymerization,such as addition polymerization and condensation polymerization.Examples of the polymerizable carbon-containing compound includecarbohydrates and a monomer.

The carbohydrates used in an embodiment of the present invention includemonosaccharides, oligosaccharides, and polysaccharides. Thecarbohydrates may be monosaccharides, oligosaccharides, polysaccharids,or a mixture thereof. Representative examples of the monosaccharidesinclude glucose, fructose, mannose, galactose, ribose, and xylose. Thesematerials may be used alone or in a combination of two or more. Theoligosaccharides are carbohydrates composed of two or moremonosaccharides joined together by a glycoside bond. Saccharides fromdisaccharides composed of two monosaccharides to decasaccharidescomposed of ten monosaccharides are collectively calledoligosaccharides. The oligosaccharides include simple ones, which arecomposed of one type of monosaccharide, and complicated ones, which arecomposed of two or more types of monosaccharides. Of theoligosaccharides, disaccharides are mainly present in the natural worldin an isolated state. Specific examples of the disaccharides includesucrose contained in sugar canes, maltose (malt sugar), which is adigested material of starch by amylase and is a raw material of wheatgluten, and lactose (milk sugar) contained in the milk of mammals.

Reducing groups of the saccharides and hydroxy groups of saccharides orcompounds other than the saccharides may undergo dehydrationcondensation.

Representative examples of monomers that may be used as thepolymerizable carbon-containing compound include furfuryl alcohol,divinylbenzene, phenol-formaldehyde, resorcinol-formaldehyde, benzeneand anthracene.

The method of filling the carbon precursor in the pores of the templatewill now be described in detail. First, a carbon precursor sol, which isa mixture of the polymerizable carbon-containing compound with acarrier, is impregnated into the pores of the template. Then, thepolymerizable carbon-containing compound in the template is polymerizedto form a polymer of the polymerizable carbon-containing compound in thepores of the template.

The carrier maybe in a liquid state and acts as a solvent, dissolvingthe polymerizable carbon-containing compound, and as a medium carryingthe polymerizable carbon-containing compound to the pores of thetemplate. The carrier may be selected from water, an organic solvent, ora mixture thereof. The organic solvent may be alcohol such as ethanoland acetone. However, furfuryl alcohol may be used as the polymerizablecarbon-containing compound or as the carrier.

An acid may be further added during the preparation of the carbonprecursor sol. The acid may promote the polymerization of the carbonprecursor. The acid may be selected from sulphuric acid, hydrochloricacid, nitric acid, sulfonic acid, or derivative or mixture thereof.Representative examples of the sulfonic acid include methylsulfonicacid.

The concentrations of the respective constituents in the mixture are notspecifically limited as long as the purpose of the present invention canbe accomplished. For example, the concentrations of the respectiveconstituents in the mixture may be as follows.

The concentration of the carrier may be about 300 to about 1000 parts byweight based on 100 parts by weight of the polymerizablecarbon-containing compound. If the concentration of the carrier is lessthan about 300 parts by weight based on 100 parts by weight of thepolymerizable carbon-containing compound, impregnation of the mixtureinto the template may not be performed easily. If the concentration ofthe carrier is greater than about 1000 parts by weight based on 100parts by weight of the polymerizable carbon-containing compound, theamount of carbon filled in the template may be reduced detrimentally.

The concentration of the acid may be about 1 to about 30 parts by weightbased on 100 parts by weight of the polymerizable carbon-containingcompound. If the concentration of the acid is less than about 1 part byweight based on 100 parts by weight of the polymerizablecarbon-containing compound, the effect of promoting the polymerizationof the polymerizable carbon-containing compound due to the addition ofthe acid may be minimal. If the concentration of the acid is greaterthan about 30 parts by weight based on 100 parts by weight of thepolymerizable carbon-containing compound, the effect of promoting thepolymerization of the polymerizable carbon-containing compound due tothe addition of the acid may be diminished.

The polymerization of the polymerizable carbon-containing compound inthe pores of the template may be performed by, for example,heat-treatment or UV irradiation. When the polymerization is performedby heat-treatment, the heat-treatment temperature of the CNT-mesoporoussilica composite impregnated with the mixture may be about 50° C. toabout 250° C. If the heat-treatment temperature is less than about 50°C., the polymerizable carbon-containing compound may not be sufficientlypolymerized. If the heat-treatment temperature is greater than about250° C., the uniformity of the resulting carbon precursor may bedecreased. The heat-treatment may also comprise a first heat-treatmentand a second heat-treatment. For example, the first heat-treatment maybe performed at about 50° C. to about 150° C. and the secondheat-treatment may be performed at about 150° C. to about 250° C. Uponcompletion of the heat-treatment processes, the carbon precursor shouldbe polymerized and the liquid carrier should be vaporized.

The above impregnation and heat-treatment may be repeated. That is,after the polymerization, the dried template may be impregnated with asecond prepared carbon precursor sol and then heat-treated as describedabove.

Thus, after polymerization, the carbon precursor impregnated in theCNT-mesoporous silica composite is carbonized by the thermaldecomposition, resulting in a carbon-CNT-mesoporous silica composite.The thermal decomposition may be performed, for example, by heating thetemplate having the carbon precursor impregnated therein at about 600°C. to about 1400° C. under a non-oxidizing atmosphere. If thetemperature is less than about 600° C., a complete carbonization may notoccur, and thus the carbon-CNT-silica composite may not be completelyformed. If the temperature is greater than about 1400° C., carbon can bethermally decomposed or the structures of the materials used in theCNT-mesoporous silica composite template may be changed. Thenon-oxidizing atmosphere may be selected from a vacuum, a nitrogenatmosphere, or an inert gas atmosphere, for example. During thisprocess, the carbon precursor is carbonized and the carrier and acid, ifused, are removed via evaporation or decomposition.

After thermal decomposition converts the carbon precursor filled in thetemplate to the carbon-CNT-silica composite, the silica is removed bytreating the composite with a solution capable of dissolving silica. Asolution capable of dissolving silica is defined as a solution thatdissolves only the silica from the carbon-CNT-mesoporous silicacomposite. Examples of a solution capable of dissolving only silicainclude an aqueous hydrofluoric acid (HF) solution and an aqueous sodiumhydroxide solution. It is known that silica is converted to a solublesilicate by alkaline fusion or carbonate melting and reacts with HF toform erodible SiF₄. Once the silica is dissolved and removed, theCNT-mesoporous carbon composite remains.

The concentration of the CNTs in the CNT-mesoporous carbon composite maybe about 0.6% to about 20% by weight. If the concentration of the CNTsis less than about 0.6% by weight, a positive effect of the CNTs on anincrease in electrical conductivity cannot be expected. If theconcentration of the CNTs is greater than about 20% by weight, theCNT-mesoporous carbon composite cannot be easily prepared since theCNT-mesoporous silica composite cannot be easily prepared.

A supported catalyst using a CNT-mesoporous carbon composite as asupport according to an embodiment of the present invention will now bedescribed.

The supported catalyst comprises a CNT-mesoporous carbon composite withmetal catalyst particles uniformly supported on the CNT-mesoporouscarbon composite. The CNT-mesoporous carbon composite may have mesoporeswith an average diameter of about 2 nm to about 10 nm, and it may have aspecific surface area of about 800 m²/g to about 3500 m²/g, Thecatalytic metal that can be used for the supported catalyst according toan embodiment of the present invention is not specifically limited andspecific examples thereof include titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),is zinc (Zn), aluminium (Al), molybdenum (Mo), selenium (Se), tin (Sn),platinum (Pt), ruthenium (Ru), palladium (Pd), tungsten (W), iridium(Ir), osmium (Os), rhodium (Rh), niobium (Nb), tantalum (Ta), lead (Pb),or a mixture thereof.

The catalytic metal may be appropriately selected depending on aspecific reaction to which the supported catalyst is to be applied.Also, the catalytic metal may be a single metal or an alloy of two ormore metals.

Specifically, when the supported catalyst is used in a catalyst layer ofa cathode or an anode of a fuel cell, such as a phosphoric acid fuelcell (PAFC) and a proton exchange membrane fuel cell (PEMFC), Pt may begenerally used as the catalytic metal. When the supported catalyst isused in a catalyst layer of an anode of a direct methanol fuel cell(DMFC), a Pt—Ru alloy may be generally used as the catalytic metal,where the atomic ratio of Pt—Ru may be typically about 0.5:1 to about2:1. Further, when the supported catalyst is used in a catalyst layer ofa cathode of DMFC, Pt may be generally used as the catalytic metal.

The catalytic metal particles may have an average particle size of about1 nm to about 5 nm. If the average particle size of the catalytic metalparticles is less than about 1 nm, the catalyst may not catalyse thecatalytic reaction. If the average particle size of the catalytic metalparticles is greater than about 5 nm, the reaction surface area of thecatalytic metal particles is relatively small and the catalytic activityis decreased.

The concentration of the metal catalyst particles in the supportedcatalyst may be about 40% to about 80% by weight. If the concentrationof the metal catalyst particles in the supported catalyst is less thanabout 40% by weight, the catalyst may be insufficient for use in a fuelcell. If the concentration of the metal catalyst particles in thesupported catalyst is greater than about 80% by weight, the cost toproduce a fuel cell with high quantities of metal particles isincreased.

To prepare the supported catalyst according to an embodiment of thepresent invention, various known methods to one skilled in the art canbe used. For example, the supported catalyst can be prepared byimpregnating the support with a solution of the catalytic metalprecursor and reducing the catalytic metal precursor. Since such methodis well-known, the detailed description thereof will not be providedherein.

A fuel cell according to an embodiment of the present invention will nowbe described in detail.

The fuel cell comprises a cathode, an anode, and an electrolyte membraneinterposed between the cathode and the anode, wherein the cathode, theanode, or both the cathode and the anode comprise the supported catalystaccording to the previous embodiment.

Examples of the fuel cell of the present invention include a PAFC, aPEMFC, or a DMFC. The structures of the fuel cells and methods ofmanufacturing such fuel cells are not specifically limited, and manyexamples thereof are wellknown to one skilled in the art. Thus, detaileddescriptions thereof will not be provided herein.

Hereinafter, the present invention will be described in more detail withreference to the following examples. These examples are given for thepurpose of illustration and are not intended to limit the scope of theinvention.

Example and Comparative Example Preparation of a CNT-Mesoporous SilicaComposite

(A) Example: 5.0 g of a surfactant Triton X-100 (Aldrich) was dissolvedin 200 ml of water, and then 0.14 g of single-walled CNTs (SWNTs) wasadded to the obtained solution and mixed. 48.4 g of tetraethoxysilane(TEOS) was dissolved in the resultant solution, and 300 ml of water and85 g of a 35% hydrochloric acid solution were added to the resultantmixture. The mixture was stirred at 40° C. for 2 hours.

Then, the resultant product was heated in an oven at 100° C. for 2hours. The powders thus obtained were filtered through a filter paperand washed twice with water. The washed powders were dried at roomtemperature for 24 hours and calcined in a reaction furnace at 550° C.for 10 hours to obtain a CNT-mesoporous silica composite. FIGS. 1A and1B are a scanning electron microscopic (SEM) photo and a transmissionelectron microscopic (TEM) photo, respectively, of the resultantCNT-mesoporous silica composite. FIG. 1B shows a CNT contained insilica.

(B) Comparative Example: A mesoporous silica material was prepared inthe same manner as described above, except that SWNTs were not used.

Preparation of a CNT-Mesoporous Carbon Composite

(C) Example: 0.94 g of sucrose was dissolved in 3.75 ml of water andthen 0.11 g of sulfuric acid was added to the resultant solution andmixed well to obtain a carbon precursor sol. Then, 1 g of theCNT-mesoporous silica composite obtained above was mixed with the carbonprecursor sol. The resultant product was heat-treated in an oven at 160°C. for 2 hours. Then, a carbon precursor sol freshly prepared was addedto the heat-treated product, wherein the amount of the carbon precursorsol added was 60% of the amount of the carbon precursor sol initiallyadded, and then heat-treated again at 160° C. for 2 hours.

Then, the heat-treated product was thermally decomposed at 900° C. undera nitrogen atmosphere. A ramp rate was 15° C./min. The resultantcarbon-CNT-mesoporous silica composite was added to HF and mixed well toremove the silica.

The CNT-mesoporous carbon composite from which the silica was removedwas isolated, washed, and dried to obtain the desired CNT-mesoporouscarbon composite.

(D) Comparative Example: A mesoporous carbon material was prepared inthe same manner as described in (C), except that the mesoporous silicamaterial obtained in (B) was used instead of the CNT-mesoporous carboncomposite obtained in (A).

FIG. 2A illustrates X-ray diffraction (XRD) patterns of theCNT-mesoporous silica composite prepared in (A) (Example) and themesoporous silica material not containing CNTs prepared in (B)(Comparative Example). FIG. 2B illustrates XRD patterns of theCNT-mesoporous carbon composite prepared in (C) (Example) and themesoporous carbon material prepared in (D) (Comparative Example). Theshapes and positions of the peaks in the XRD patterns confirmed thatpores with uniform structures were arranged.

FIG. 3 illustrates XRD patterns of products in the steps of thepreparation method of the CNT-mesoporous carbon composite in (C), i.e.,the calcined CNT-mesoporous silica composite, a combination of theCNT-mesoporous silica composite and the carbon-CNT-silica composite, andthe CNT-mesoporous carbon composite after removing the silica using HF.In all the three cases, a peak corresponding to the CNTs was clearlyobserved, which indicates that the CNTs were neither modified nor lostthroughout the steps of the preparation method.

Nitrogen adsorption tests were performed for the CNT-mesoporous carboncomposite prepared in (C) (Example) and the mesoporous carbon materialprepared in (D) (Comparative Example). The results are shown in Table 1.

TABLE 1 Example Comparative Example Specific surface area 2207 2970(m²/g) Pore diameter (nm) 3.65 3.85

The data in Table 1 confirms that there was no remarkable difference ina pore diameter between the CNT-mesoporous carbon composite prepared in(C) (Example) and the mesoporous carbon material prepared in (D)(Comparative Example), but the mesoporous carbon material prepared in(D) (Comparative Example) possessed a greater specific surface area thanthe CNT-mesoporous carbon composite prepared in (C) (Example).

Preparation of a Pt-Supported Catalyst

(E) 0.5 g of the CNT-mesoporous carbon composite prepared in (C)(Example) was placed in a plastic bag, and then 0.9616 g of H₂PtCl₆ wasweighed and dissolved in 1.5 mL of acetone in a beaker. The obtainedsolution was mixed with the carbon support in the plastic bag. Themixture was dried in air for 4 hours, and then was transferred to acrucible and dried in an oven at a temperature of 60° C. overnight.Then, the crucible was placed in an electric furnace with nitrogenflowing and the nitrogen was allowed to flow for 10 minutes. Next,nitrogen gas was replaced with hydrogen gas and the temperature in theelectric furnace was raised from room temperature to 200° C. andmaintained for 2 hours to reduce a Pt salt supported on theCNT-mesoporous carbon composite. The hydrogen gas was replaced withnitrogen gas and the temperature in the electric furnace was raised to250° C. at a rate of 5° C./min, maintained at 250° C. for 5 hours, andthen cooled to room temperature. Thus, a catalyst supported on theCNT-mesoporous composite, with a concentration of Pt supported equal to60% by weight, was obtained.

(F) A catalyst supported on a carbon material, with a concentration ofPt supported equal to 60% by weight, was prepared in the same manner asdescribed in (E), except that the mesoporous carbon material prepared in(D) (Comparative Example) was used instead of is the CNT-mesoporouscarbon composite prepared in (C) (Example).

FIG. 4 illustrates XRD patterns of the supported catalysts prepared in(E) (Example) and (F) (Comparative Example). The average particlediameter of the Pt catalyst supported on the CNT-mesoporous carboncomposite prepared in (C) (Example) was 4.8 nm, while the averageparticle diameter of the Pt catalyst supported on the mesoporous carbonmaterial prepared in (D) (Comparative Example) was 4.5 nm.

Preparation of a Fuel Cell

(G) The supported catalyst prepared in (E), in which the CNT-mesoporouscarbon composite was used as a support, was dispersed in a dispersionsolution Dupont-brand Nafion® 115 in isopropyl alcohol to prepare aslurry and was coated on a carbon electrode using a spray process so asto obtain a concentration of 3 mg/cm² of the coated catalyst, measuredby Pt concentration. Then, the electrode was passed through a rollingmachine to enhance adhesion between the catalyst layer and carbonelectrode, thereby obtaining a cathode. An anode was prepared using acommercially available Pt—Ru Black catalyst and a unit cell was preparedusing the cathode and the anode.

(H) A unit cell was prepared in the same manner as described in (G)(Example), except that the supported catalyst prepared in (F)(Comparative Example), in which the mesoporous carbon material was usedas a support, was used instead of the supported catalyst prepared in (E)(Example).

Performances of the unit cells obtained above were measured at 50° C.while excessively supplying 2 M methanol and air. The results are shownin FIG. 5. Although the CNT-mesoporous carbon composite prepared in (C)(Example) has a smaller specific surface area than the mesoporous carbonmaterial prepared in (D) (Comparative Example) as described above, theunit cell prepared using the CNT-mesoporous carbon composite prepared in(C) (Example) has a higher current density at equivalent cell potentialsthan the unit cell prepared using the mesoporous carbon materialprepared in (D) (Comparative Example).

As described above, a CNT-mesoporous carbon composite according to thepresent invention can be prepared using a CNT-mesoporous silicacomposite as a template. The CNT-mesoporous carbon composite has a highelectrical conductivity due to the CNTs contained therein. Thus, whenthe CNT-mesoporous carbon composite is used in an electrode of a fuelcell, the fuel cell has a remarkably improved performance relative tothe conventional catalyst support that does not contain CNTs.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A carbon nanotube (CNT)-mesoporous silicacomposite comprising: mesoporous silica; and CNTs dispersed in themesoporous silica.
 2. The CNT-mesoporous silica composite of claim 1,wherein the concentration of the CNTs is from about 0.3% to about 10% byweight, based on to the total weight of the CNT-mesoporous silicacomposite.
 3. A method of preparing a carbon nanotube (CNT)-mesoporoussilica composite, the method comprising: adding CNTs to water and adissolved surfactant, to form a mixture; adding a silica source andwater to the mixture to form a solution; adding an acid to the solutionto adjust the pH of the solution; stirring the solution; heating thesolution to obtain a powder; separating the powder from the solution;washing the powder at least once; and calcining the powder to obtain aCNT-mesoporous silica composite.
 4. The method of claim 3, wherein theconcentration of the surfactant is from about 1,000 to about 100,000parts by weight, based on 100 parts by weight of the CNTs.
 5. The methodof claim 3, wherein the concentration of the silica source is from about3,000 to about 300,000 parts by weight, based on 100 parts by weight ofthe CNTs.
 6. The method of claim 3, wherein the silica source consistsof tetraethoxysilane, tetramethoxysilane, or sodium silicate.
 7. Themethod of claim 3, wherein: the pH of the solution is adjusted to fromabout 0.7 to about 7.0; and the acid is nitric acid, hydrochloric acid,sulfuric acid, or acetic acid.
 8. The method of claim 3, wherein theheating is performed at from about 80° C. to about 160° C.
 9. The methodof claim 3, wherein the heating is performed for about 30 minutes toabout 120 minutes.
 10. The method of claim 3, wherein the separating isperformed by filtration or centrifugation.
 11. The method of claim 3,wherein the calcining is performed at from about 300° C. to about 550°C.
 12. The method of claim 3, wherein the calcining is performed forfrom about 3 hours to about 15 hours.
 13. The method of claim 3, whereinthe CNTs are single-walled CNTs, multi-walled CNTs, carbon nano-fibers,or any combination thereof.
 14. The method of claim 3, wherein the CNTsare regularly dispersed in the CNT-mesoporous silica composite.
 15. TheCNT-mesoporous silica composite of claim 1, wherein the CNTs areregularly dispersed in the mesoporous silica.